1. Field of the Invention
This invention relates to radar systems, and more particularly, to moving target indicator systems of the digital Doppler type. More particularly, the present invention relates to a system which adjusts or adapts itself to a maximum cancellation of "moving clutter".
2. Description of The Prior Art
Moving target indicator radars, per se, have long been known. The general subject of MTI and pulse-Doppler radar (the latter being a category into which the present invention may be said to generically reside) is presented in Chapter 4 of the textbook "Introduction to Radar Systems" (1962) by Merrill I. Skolnik (a McGraw Hill book). Another book by the same author and publisher, entitled "Radar Handbook" (1970), also discusses the subject in its Chapter 19. Also, a discussion in Chapter 35 of the latter identified reference under the title Digital Signal Processing is germane in that the present invention is, broadly speaking, a type of digitally processed Doppler radar system.
Yet another reference of background interest in the present connection, is U.S. Pat. No. 3,441,930, entitled "Doppler Radars". That reference describes the subject of digital encoding of amplitudes of signal within discrete range increments. The said range increments represent intervals of duration on the order of the system transmitted pulse, and hence, a relatively large number of these occur successively during each pulse repetition period of the radar system.
Digital processing of signals in a Doppler radar affords certain well known advantages. Among these is inherent adaptability to staggered or other types of variable PRF systems. Ordinarily, analog delay devices used in signal comparison in MTI systems are not adapted to variable PRF systems without great complexity and unusually stringent stability requirements. Moreover, in recent times, the refinement of digital components and the subminiaturization of such devices as memories, shift registers, counters and other multi-channel or multi-digit subsystems is making digital instrumentation of radar systems particularly attractive and increasingly economical.
A modern moving target indicator radar system must not only be adapted to variable PRF operation (for elimination of blind speeds and for other reasons) but must also account for such extrinsic factors as motion of the platform upon which the radar system operates. coordinate.
One of the particular problems of the prior art concerns identifications of bona fide targets in the presence of such moving clutter as chaff, hydrometeroic phenomena, and terrain features exhibiting apparent motion because of the actual motion of the radar platform in the range corrdinate. Radar system instrumentations have heretofore employed selective Doppler band-pass control and other such means, but have not addressed themselves to the more sophisticated aspects of design for operation in these situations.
The manner in which the present invention solves problems of the prior art and uniquely advances the art of instrumenting modern pulsed digital Doppler MTI systems will be more fully understood as this description proceeds.